NOTATIONS
CHAPTER 3 MATERIALS AND METHODS
3.5 TEST METHODS
3.5.4 Tests for Engineering Properties
Compaction behaviour
Light compaction tests are done on samples of expansive soil, fly ash and their mixtures.
These tests are conducted using a small compaction apparatus developed and verified by Prashanth (1998). The schematic diagram of this compaction apparatus is produced in Fig. 3.11.
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The main features of this mini-compactor vis-à-vis the Standard Proctor (light compaction) test are:
i. For each test, approximately 200 g of dry soil is required and for each set of 6 moisture content conditions, approximately 1.2 kg of soil is required. For Standard Proctor test, approximately 2.5 kg of soil is required.
ii. Each test of each set is done with fresh soil, i.e. soil is not re-used.
iii. The soil is compacted in three layers using a 0.8 kg drop weight falling through 160 mm, as compared to 2.6 kg weight falling through 310 mm. Number of tampings in each layer is 45 compared with 25 tampings in Standard Proctor test.
Fig. 3.11 Compaction apparatus (Prashanth, 1998).
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iv. There is substantial saving in test material. Since sample mixing time is more than the testing time for most of the tests, this results in substantial reduction in sample preparation time.
v. Unlike the Proctor test, the sample in the mini compaction device is completely confined at its top by the hammer foot, the bulging during compaction is prevented.
vi. The drop weight does not fall on the soil directly, but the load is transferred through a foot. Thus some amount of kinetic energy of the falling weight is lost by way of sound, vibration, etc. For this, more energy is required for compaction of the same quantity of soil using this test (1.49 J per cm3 of compacted soil) compared to that required in Proctor’s test (0.592 J per cm3 of compacted soil).
vii. The internal diameter of the compaction cylinder is 38 mm. Hence, 38 mm diameter compacted samples can be obtained from this test for other tests such as UC test, triaxial test, etc.
The moisture content vs. dry density curves are plotted to find the optimum moisture content (OMC) and maximum dry density (MDD) in the same fashion as in the case of Proctor test.
For verification of the miniature compaction apparatus, some tests were carried out using the Standard Proctor compaction and the mini compaction apparatus. It may be observed that the compaction curves from both the devices almost match each other (Fig. 3.12). It establishes that the mini compaction apparatus can be used satisfactorily in lieu of the Standard Proctor test. Since this mini compaction apparatus requires much less soil, time and effort compared to the conventional one, in the present study it is used for all compaction tests.
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Fig. 3.12 Comparison of Standard Proctor and mini compaction test results.
At first, OMC and MDD are determined for the expansive soil-fly ash mixes without addition of lime, with fly ash contents of 0%, 20%, 40%, 60%, 80%, and 100%. Then OMC and MDD are found out for the lime-treated soil-fly ash mixes for the same fly ash contents and with lime contents of 1%, 3%, 5%, 9%, 13% and 17%. For lime treated soils, a 1-hour period was kept between the start of water mixing and start of compaction test to allow for the initial lime reactions with soil to take place. This delay was adopted because it is not possible to perform compaction tests exactly immediately after mixing.
The process of mixing water to the prepared soil takes about 15 minutes. As water is sprayed gradually for mixing, some particles will get more reaction time than others if compaction is done immediately, i.e. after about 15 minutes from the start of mixing. If tests are done with some delay, say of 1 hour, the difference of reaction time of different portions of the sample will be leveled off. This is also expected to contribute to the
10 11 12 13 14 15
0.0 10.0 20.0 30.0 40.0 50.0
Dry density,γd(kN/m3)
Moisture content (%)
Proctor F90 Proctor F50 Proctor F10
mini F90 mini F50 mini F10
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uniform spread of moisture in the sample. To find out the differences in OMC and MDD due to delay, some tests were also done without delay.
The ES-FA mixes with 1% and 3% lime were tested immediately after mixing (within 15 minutes of starting mixing) and also with a delay of 1 hour to see the difference in compaction due to delay effect. The results are shown in Fig.3.13 and Fig.3.14.
In the case of samples with 1% lime content, the OMC was found to be slightly higher for 1 hour delay than immediate values. This was contrary to the findings of Osinubi and Nwaiwu (2006). In case of 3% lime addition, OMC of 1 hour delay tests were slightly higher in case of 0-40% fly ash contents. For higher fly ash soils, the results followed findings of Osinubi and Nwaiwu (2006). The differences in MDD for immediate and 1h delay tests are marginal. In both cases of 1% lime and 3% lime, the MDD was slightly less in case of delayed compaction, except for mixes with higher fly ash contents with 3% lime.
Fig. 3.13 Delay effect on OMC for ES-FA mixes with 1% and 3% lime.
15 20 25 30 35 40 45
0 20 40 60 80 100
Optimum moisture content (%)
Fly ash content (%)
L1 immediate L1 1hour
L3 immediate L3 1hour
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Fig. 3.14 Delay effect on MDD for ES-FA mixes with 1% and 3% lime.
Consolidation behaviour
One-dimensional consolidation tests are done on mixes of expansive soil and fly ash with or without lime treatment. The tests were done according to IS:2720 (Part 15) – 1986.
Fixed ring type oedometers were used. All specimens were prepared at OMC and MDD.
The pressures applied were 10, 20, 40, 80, 160, 320, 640 and 1240 kPa above a seating pressure of 5 kPa. Each pressure was sustained for 24 hours and time-deformation records obtained. Total settlement was recorded for each pressure, from which pressure- settlement characteristics were obtained. Compression index of each of the mix was determined from the voids ratio versus log(pressure) plots.
Swell behaviour
Free Swell Indices of soil-fly ash mixes with and without lime treatment are found out as per IS:2720 (Part 40) – 1977. The free swell index is the ratio of volume of 10 g of soil submerged in water in an 100 ml measuring cylinder to the volume of same quantity of
11 12 13 14
0 20 40 60 80 100
Maximum dry density (kN/m3)
Fly ash content (%)
L1 immediate L1 1hour
L3 immediate L3 1hour
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soil submerged in kerosene. Swelled volume is also calculated and reported as volume per g of swelled soil without comparing with volume in kerosene.
Swelling was also observed under a seating pressure of 5 kPa in samples remoulded and mounted on oedometers as per IS:2720 (Part 41) – 1977. Samples were prepared at OMC and MDD. The increase in sample height has been recorded until swelling is stabilized.
The swell percentage is then determined as the ratio of increase in sample thickness to the original thickness expressed in percentage. The soil after exhibiting the maximum swell has been incrementally reloaded to bring it back to its original thickness of 20 mm.
The cumulative load at which the swelled soil attains the original thickness has been used to determine the swelling pressure of the soil.
Strength
Unconfined compressive tests are conducted as per IS: 2720 (Part 10) – 1991. Samples of soil-fly ash mixes with or without lime treatment are prepared at OMC and MDD. The samples with lime are cured for different periods (0, 1, 3, 7, 15, 30, 60 and 90 days), to see the effect of curing on strength. The 38mm diameter specimens are compressed at a strain rate of 1.25 mm/min. The peak compressive stress attained by a specimen is considered as its unconfined compressive strength, and the corresponding strain is considered as the failure strain.